The present invention provides a humeral head resection guide. Specifically, this invention relates to a guide to position a cutting blade at a set angle and height for correct orientation of the osteotomy cut of the head of the humerus with respect to the humeral intramedullary axis.
The humerus is a long bone of the upper limb which forms the shoulder joint at its proximal end, where its head articulates with the glenoid cavity of the scapula. The head is nearly hemispherical in form, generally smooth and rounded, and coated with a smooth, durable covering of articular cartilage. The head articulates with the glenoid fossa of the scapula as a ball and socket joint; the joint being lined with a thin, inner lining, the synovium, for smooth movement. The ball and socket joint enables raising, twisting, bending, and forward, side, and backward movement of the arm. Muscles and tendons surrounding the joint provide stability and support.
Arthritis or other degenerative joint diseases may cause the joint surface, e.g. the surface of the humeral head, to be destroyed by wear and tear, inflammation, injury, or previous surgery. Such joint destruction causes the shoulder to become stiff, painful and generally unable to carry out its normal functions. Joint destruction may also be caused by fractures. Whatever the origin, joint damage in the shoulder may necessitate resection and replacement of the humeral head with a prosthetic device.
The goal of shoulder replacement arthroplasty is to restore the best possible function to the joint by removing scar tissue, balancing muscles, and reconstructing the destroyed joint surfaces with artificial ones. Prosthetic implant devices for use in reconstructing the proximal area of the humerus are designed to mimic the natural bone anatomy of the proximal end of the humerus. The prostheses often are modular and include a stem to be fitted to a resected humerus and a head sized and configured to approximate the humeral head. Optionally, one or more connecting members may be used to connect the stem to the head in a variety of configurations. The head portion of the prosthesis generally extends angularly from the stem portion, and the angle and length of the extension may be modified with the connecting members. It is noted, of course, that unitary prostheses or modular prostheses comprising only stem and head components are also used.
The humeral head component of a prosthesis typically has a generally spherical surface on one side and a flat face on the opposite side. The spherical surface replaces the bearing surface of the normal humeral head to allow movement of the shoulder.
It is frequently difficult to establish the proper position and orientation for the implant in the humerus. The surgery to implant a humeral prosthesis involves performance of an osteotomy to accommodate the size and structure of the prosthesis. The osteotomy cut must be made as precisely as possible so that the angle of the cut corresponds to the angle between the stem and head components of the prosthesis. In addition, the rotation of the cut may vary to adjust to bone wear or capsular looseness. Another important variable in proper positioning of the humeral head component is the rotational position, or retroversion, of the head on the humerus. Anatomically, the average retroversion between a plane defined by the perimeter of the anatomical head and the axis of the flexed forearm is approximately 30 degrees. Typically, it has been difficult to reliably reproduce desired retroversion. Establishing correct retroversion is important because incorrect retroversion may lead to problems with subsequent joint dislocation. It is also necessary to establish the correct height of the implant on the humeral shaft. Excess height may create too much tension in the deltoid muscle, while inserting the implant too far down the humerus may result in deltoid lag.
From a surgical standpoint, the humeral head osteotomy cut may be guided by a resection guide. A trial prosthesis may also be placed along the proximal humeral shaft as a guide for proper inclination of the osteotomy. The possibility of error inherent in this free hand approach makes it problematic. Inaccurate resection, even by a small amount, may result in an ill-fitting prosthesis which may cause complications for the patient and may eventually require replacement of the prosthetic device.
Humeral cutting guides have been introduced that aid in the resection of the humeral head. One such cutting guide is disclosed in U.S. Pat. No. 5,108,396 for INTRAMEDULLARY REFERENCED HUMERAL HEAD RESECTION GUIDE, Lackey et al. The guide includes an intramedullary alignment member having a longitudinal axis and structured for substantial axial alignment with the intramedullary canal of the bone. The guide also includes an extramedullary alignment member and a collar rotatably mounted on the intramedullary alignment member for rotating the extramedullary alignment member about the longitudinal axis of the intramedullary alignment member. This rotation allows the extramedullary alignment member to provide a guide for a desired degree of humeral retrotorsion by manipulating the patient""s forearm so that it is substantially parallel to the extramedullary alignment member. A cut block and a first shaft and a second shaft in a perpendicular orientation relative to the first shaft for positioning the cut block in a desired orientation relative to the head of the bone are also provided.
Another guide is disclosed Dale et al. in U.S. Pat. No. 4,893,619 for HUMERAL OSTEOTOMY GUIDE. The device includes a proximal end saw guide for defining an osteotomy saw line on the proximal end of the humerus and a distal end mechanism for stably aligning the saw guide on the proximal end of the humerus, such as a distal cross arm having a slot therethrough. The saw guide engages a selected surface on the proximal end of the humerus and supports the proximal end of a radial arm above the humerus. The mechanism for aligning, or cross arm, engages the distal end of the humerus and supports the distal end of the radial arm above the humerus.
U.S. Pat. No. 5,961,555 for MODULAR SHOULDER PROSTHESIS to Huebner discloses a targeting/installation instrument and a modular shoulder prosthesis including a head and a stem. The instrument includes a template member to which are mounted a mounting bar, a height adjusting mechanism, and a retroversion guide. This establishes the correct alignment between the template and the implant. It is noted that the guide is aimed primarily at placing the prosthesis after the cut has been made.
Further, U.S. Pat. No. 6,168,627 for SHOULDER PROSTHESIS, Huebner discloses a shoulder prosthesis including a shoulder prosthesis having a head and an elongate stem portion including a proximal end, a distal section, and an alignment section. The alignment section includes a plurality of reference marks positioned to facilitate placement of the prosthesis in the bone at a previously determined position. A targeting/installation instrument is provided substantially as disclosed in the ""555 patent. Additionally, installation and alignment of the implant may be facilitated by placing indications or reference marks on the implant.
The present invention relates to an apparatus for guiding the resection of the head of the humerus. Specifically, the invention relates to a humeral resection guide that holds a cutting blade at a set angle and position for removing the humeral head. In a preferred embodiment, the guide includes a base, a cut block, and a stylus. The base is configured for rotatable connection with a tool defining the axis of the humerus. The tool may be a reamer or other device that is inserted into the intramedullary canal of the humerus with a shank of the tool extending superiorally above the head of the humerus to establish the axis of the humerus. A cut block is operatively connected to the base and includes a component for receiving a saw blade. A stylus is provided to engage the cut block and extend around the articular margin of the humeral head for alignment with the superior and posterior margins of the humeral head. Optionally, a version gauge may be provided.
The base of the resection guide is configured to be inserted over the shank of the reamer or tool. Preferably, the base includes a bore for receipt of the shank. The base is rotatable about the axis of the humerus, as defined by the reamer or tool, and may be rotated slightly about the axis to provide the proper amount of humeral version. A version gauge may be provided to reference for precise alignment of the base for rotation. The base includes an outwardly and downwardly extending arm, the downwardly extending portion of the arm being roughly parallel to but spaced from the axis of the reamer. Attached to the bottom of the downwardly extending arm of the base is the cut block, the latter having a component for attachment to or receiving of a surgical saw blade. This component may be a slot for receiving and guiding a surgical saw blade.
The cut block is configured for fixation to the humerus, for example, by having a number of small openings through which pins may be inserted. The stylus attaches to the cut block and extends around the articular margin of the humeral head. Any suitable attachment of the stylus to the cut block may be used. Preferably, the stylus attachment includes a tab of the stylus extending into a saw-receiving slot of the cut block. The section of the stylus extending around the articular margin of the humeral head includes a portion for alignment with the superior margin of the humeral head, and another portion for alignment with the posterior margin of the humeral head. The portions for alignment may comprise fiducial tabs.
By rotating the base about the axis; moving the base upwardly and downwardly on the axis; and adjusting the position of the stylus, for example by moving the tab inwardly and outwardly of the saw blade slot; the stylus may be positioned precisely with an alignment portion aligned with the superior margin of the humeral head, and an alignment portion aligned with the posterior margin of the humeral head. The position of the humeral head is thus adjusted precisely with respect to the cut block.
In use, the base slides over and locks to the canal reamer or tool. Before locking the base to the canal reamer or tool, version and height are set by rotating and sliding the base about the axis. When the alignment portions of the stylus are aligned with the superior and posterior margins of the humeral head, the base is locked. Once the base has been locked to the reamer or tool with the cut block at the desired version and height, the version gauge may be rotated about the base and aligned with a reference mark on the reamer or tool.